Fabrication and Application of Self-masked Silicon Nanostructures in Deep Reactive Ion Etching Processes
Silicon Grass is a nano-scale surface modification formed by self-organizing processes in plasma etching. It can be used to enable new functionalities or enhance the performance of MEMS, Biological MEMS or MOEMS. Its low-cost generation with standard fabrication equipment makes it a promising research subject. The thesis investigates the formation, modification and application of Silicon Grass resulting from the cyclic Deep Reactive Ion Etching process (c-DRIE). The main goal is the controlled generation as well as the modification of the Silicon Grass. Therefore, the work focuses on three main subjects: nanomasking - the self-organized mechanism initiating Silicon Grass generation, Silicon Grass processing - for controlled structure etching and modification, and the integration and application in MEMS. In order to investigate the nanomasking process and derive a formation theory for the c-DRIE process, different morphological and chemical studies by SEM, AFM, XPS and AES as well as process analysis methods are used. It is shown that the nanomask consists of carbon-rich, filament-like clusters, whose morphology can be changed by various process parameters. The reproducible generation of a nanomask in the c-DRIE is based on the controlled abrasion of the inhibiting film. This is achieved by process control via OES allowing for the initiation of nanomasking even for varying process conditions. Various influences on nanomask formation and morphology are investigated and it is found that carbon dust formation in C4F8 polymerizing plasmas has a profound effect. It is shown that the characteristic geometrical features of the structures undergo significant changes during the Silicon Grass process. Depending on the applied process parameters, the resulting profiles and the sidewall morphology of the Silicon Grass is changed. The metallization of Silicon Grass by physical vapor deposition and electroless plating as well as the suitability of different Silicon Grass types for mechanical bonding and infrared optical applications are investigated. Finally, the integration of Silicon Grass in MEMS is discussed. Here, fundamental information about possible integration methods, requirements and limitations are given. The possible integration and practical application of Silicon Grass in MEMS is demonstrated by the fabrication of a thermo-mechanically actuated cantilever.